Pest control smoke generators



United States Farm 2,695,258 PEST CONTROL SMOKE GENERATORS No Drawing.Application June 27, 1952, Serial No. 296,068

Claims priority, application Great Britain September 14, 1951 9 Claims.(Cl. 167-40) The present invention relates to the art of fumigating withpesticidal compounds, and more particularly to the provision of animproved composition for the thermal production of fumes of pesticidalcompounds that are capable of vaporization when suitably heated. Theinvention is especially valuable for the purpose of fumigating withcombustible pesticidal compounds or pesticidal compounds easilydecomposed when overheated.

In the majority of pest control smoke generators of the kind wherein avaporizable pest control compound is as sociated with a mixture of solidingredients capable when locally sufficiently heated of undergoingself-sustained gasproducing exothermic reaction the said mixture hascomprised an organic combustible material and an inorganic oxidizingagent, the pest control compound being either mixed with theseingredients or so separated from them in the generator as to be swept bythe hot gases they produce. It is essential that the production of thestream of gases laden with the pest control compound produced by thegenerator should not be accompanied by flame as this would have theeffect of destroying the pest control compound. As the majority of pestcontrol smoke generators depending for their action on the use oforganic combustible material and inorganic oxidizing agents are of lowbiological efficiency this can be attributed to the excessively hightemperature at which these ingredients react. These ingredients are alsounable to react in the selfsustained manner if they are loaded withsuflicient pest control compound to bring down the temperature of areaction zone in the pesticidal mixture to below the decompositiontemperature of the pest control compound.

Very much better results have been obtained by employing ammoniumnitrate or guanidine nitrate in association with one or more sensitizersfor self-sustained flameless exothermic gas-producing decomposition, forwhich purpose certain chromates or dichromates have been successfullyemployed. Although the biological efficiency of pest control smokegenerating compositions based on ammonium nitrate and salts of chromicacid is high these compositions are hygroscopic and must therefore inpractice be packaged in sealed containers. The gases they produce arealso acidic, so it is on the whole often undesirable to expose forexample dyed silk or rayon articles to such smokes. They are, however,successfully employed both for disinfestation of plants in greenhousesand for the control of insects in other types of buildings, but someskill and care may be called for in their application, since the acidgases become phytotoxic if the concentration of the pesticidal fume isexcessive. The gases obtained from compositions based on sensitizedguanidine nitrate contain ammonia and so they are also phytotoxic if theconcentration of the pesticidal fume is excessive.

It is also known that pest control smoke generating compositions can beobtained from a mixture comprising a thermally vaporizable pesticidalcompound and ammonium dichromate, either alone or in association withguanidine nitrate, as the compound capable of flameless exothermicgas-producing decomposition.

Neither ammonium dichromate nor guanidine nitrate is noticeablyhygroscopic, although mixtures of the two :ompounds when stored attemperatures slightly exceedng C. tend to react with the formation ofhygroscopic tmmonium nitrate. Again, although ammonium dihromate has theadvantage that the gases produced are lmost neutral and substantiallydevoid of phytotoxicity, ieir biological efliciency is much lower thanthose of mpositions based on ammonium nitrate or guanidine compact form,

nitrate sensitized by means of a relatively small proportion of a saltof chromic acid.

It is therefore desirable to be able to produce pest control smokegenerating compositions capable of yielding substantially neutralnon-phytotoxic gases of biological efficiencies as high as thoseobtainable from known compositions.

According to the present invention a pest control smoke generatingcomposition comprising one or more vaporizable pest control compoundsand ammonium dichromate is characterized in that said compositionincludes potassium persulphate.

The gases obtained from mixtures of ammonium dichromate and potassiumpersulphate are very faintly acid, but according to a further preferredembodiment of the invention the mixture capable of self-sustainedfiameless gas-producing exothermic decomposition with which thevaporizable pest control compound is in association also contains aminor proportion of guanidine nitrate whereby the gases obtained may beadjusted to neutrality or to slight alkalinity without detriment totheir non-phytotoxic character.

The pest control smoke generating compositions of this invention are ofnon-hygroscopic character, and are of high biological efficiency. Theyyield a friable ash which retains only a very small proportion of thepest control compound and their reaction temperature tends to besomewhat lower than those of the hitherto known smoke generatingcompositions, which may to some extent account for their high biologicalefficiency.

In the composition the amount by weight of potassium persulphate. toammonium dichromate is preferably between 2:3 and 3:2. The ratio byweight of guanidine nitrate to that of the combined weights of potassiumpersulphate and ammonium dichromate is not greater than 1:4 and ispreferably of the order of 1:10, and the ratio by weight of thevaporizable pest control compound to these three ingredients mayconveniently be from 1:100 to 3:2 depending on the individuality of thepest control compound.

Suitable pest control compounds include, azobenzene, benzenehexachloride, alpha,alpha-bis(parachlorophenyl)beta,beta,beta-tri-chlorethane, hexaethyltetraphosphate, paranitrophenyldiethyl thiophosphate, Thanite per cent isobornyl-thiocyano-acetate),ortho-dichlorbenzene, tetrachlorethane, dimethylphthalate and tetraethylpyrophosphate.

A cartridge made up from a charge of the composition and a casing forsaid charge may advantageously include a small piece of fuse or of matchcomposition or other igniting composition in contact with the fumigatingcharge in order to facilitate the ignition of the latter from anordinary domestic friction match, electric fusehead or other source ofignition. The fumigating charge may be in and for its production thepulverulent mixture of ingredients may be subjected to compression;Alternatively the mixture may be made into compact form with the aid ofa binder or bonding agent, and may be extruded or moulded into form.Otherwise the fumigating charge may conveniently be lightly compacted ina cartridge having a paper or other suitable wrapper or envelope.

The compositions of the invention are illustrated by the examples setout in Table l in which all parts are by weight. In the examples thepest control compounds used are as follows:

Alpha,alpl1a bis(paraehlomphenyl) beta,beta,beta trichlorethane(technical).

Azobenzene (technical).

Parmgtrophenyl diethyl thiophosphate (crude 70 percen Azobenzeno(technieaD/Pau nitrophenyl diethyl thiophosphate (crude 70 percent).

7 Alpha,al ha biM araehIorophenyI) beta,beta,beta trichloret ane (teenlenl).

8 Hexachloroeyclohexane containing 13 percent of the gamma isomer.

Table 1 E Yam plea Active ingr Potassium persu1phate Ammoniumdichromate.

Guanidine nitrate China clay.

Sodium chloride Kieselguhr Decomposition temperature, 0

Percentage of active ingredients retained iri ash Percentage acidity ofgases as N02 Biological Elficienoy Pesticide in composition Test insectParanitrophenyl diethyl thiophosphate Azobpn one Hexachlorocyclohexaneaa bis(p.chlorophenyl) 55/3 trichlorethane aa bis(p.chloropheny1) BBBtrichlorethane Aides aegypti (larvae) -percent Tribolcumcammum'fitiIifiifiiiI Aides zzegypti (larvae) "percent" Triboleumcastancum Hbst ..percent Phytotoxlcity (test plant tomato) I Alkaline. 2Acid.

in the amount by weight of potassium persulphate to ammonium dichromateis between 2:3 and 3:2.

2. A pest control smoke generating composition as claimed in claim 1which includes a minor proportion of guanidine nitrate.

3. A pest control smoke generating composition as Composition Pestcontrolcompound claimed in claim 2 wherein the ratio by weight of thevaporizable pest control composition to the combined 1 ig 'g methyltmophosphate (crude 70 weights of potassmm persulphate, ammoniumdichromate 2 Azobenzene (technical). and guanidine nitrate is from 1:100to 3:2. 3 Hexachlorpcyclohexane containing 90 percent of the 4. A pestcontrol smoke generating composition as gamma 15mm claimed in claim 2wherein the ratio by weight of guani- 111 1 1 th giiiifigfifiifiei. examcontaining 3 percent 0 e dine nitrate to that of the comb ned weights ofpotassium 5 flexachlorpcyclohexane containing 13 Percent Of thepersulphate and ammonium dichromate is not greater gamma 15011161. I 1.46 fiexachlfirpeffihhexm contammg 90 percent of the 5 pest con rol smokegenerating composition as gamm 1S0 er. 7 Hexflchlolfmyclohexanecontaining 13 Percent Of the claimed in cla1m 4 wherein the said who 151:10. 8 fii fi g sfigg (paracmomphenyb beta beta hem 6. In a smokegenerator, a pest control smoke generattrielilorethane (technical). ingcomposition comprising at least one vaporizable pest 9nexachlorgcyclohoxafle containing 13 Percent of the control compound,ammonium dichromate, and potasgamma 011161. 10 Hexachlorocyclohexanecontaining 13 percent of the l w whe'leln g g welght b Poms gammaisomer,Sllll'l'l. peisulp ate to ammonium 1c romate 1s etween 2:3 and 3 :2.

Table 2 Composition 1 2 3 4 5 6 7 8 9 10 Active ingredient; Ammoniumnitrate Guanidine nitrate Potassium Chl'nmain Ammonium oralam Ammoniumdichromate.

Potassium nitrate.

Sodium choride Kieselgnhr.

China clay. Decomposition temperature, C

Percentage of active ingredients retained in ash 30 Percentage acidityor alkalinity of gases 3. 8 4. 5 6. 8 5. 6 6. 2 6. 4 1. 7

N02 NO: N02 N02 N02 N02 NHa Biological Efiiciency Pesticide incomposition Test insect Para-nitrophenyl diethyl thiophosphate... Aidesaem pti (larvae) percent 94 Azohnrwpnn Hexachlorocy Tr" castancumHbst... percent 77 77 85 88 36 ac! bis (paraehlorophenyl) 61 Btrichloreth- Ades aegypti (larvae) percent. 87

Phytotoxicity (test plant tomato) 4. 1 4. 5 3. 1

What we claim is: 1 A pest control smoke generating compositioncomprlslng at least one vaporlzable pest control compound,

7. A smoke generator as claimed in claim 6 wherein the charge is incontact with an igniting means.

8. A smoke generator as claimed in claim 6 wherein ammonium dichromate,and potassium persulphate, where- 35 the igniting composition is a smallpiece of fuse.

5 6 9. A smoke generator as claimed in claim 6 wherein FOREIGN PATENTSthe igniting composition is a match composition. Nu {14 G Cmntry O D ate6 reat ritain ct. 27, 1949 References Cited in the file of this patent 5636,692 Great Britain May 3 1950 UNITED STATES PATENTS Number Name Date2,557,814 Dinsdale June 19, 1951

1. A PEST CONTROL SMOKE GENERATING COMPOSITION COMPRISING AT LEAST ONEVAPORIZABLE PEST CONTROL COMPOUND, AMMONIUM DICHROMATE, AND POTASSIUMPERSULPHATE, WHEREIN THE AMOUNT BY WEIGHT OF POTASSIUM PERSULFPATE TOAMMONIUM DICHROMATE IS BETWEEN 2:3 AND 3:2.